Dye tracing

Our new paper about the application of dye tracing to investigate the flow of pollutants on Rabots glaciär has just been published online in Hydrology and Earth System Sciences Discussions, and you can find a link to it here.

Abstract:

Over 11 000 L of hydrocarbon pollution was deposited on the surface of Rabots glaciär on the Kebnekaise Massif, northern Sweden, following the crash of a Royal Norwegian Air Force aircraft in March 2012. An environmental monitoring programme was subsequently commissioned, including water, snow and ice sampling. The scientific programme further included a series of dye tracing experiments during the 2013 melt season, conducted to investigate flow pathways for pollutants through the glacier hydrological system, and to gain new insight to the internal hydrological system of Rabots glaciär. Results of dye tracing reveal a degree of homogeneity in the topology of the drainage system throughout July and August, with an increase in efficiency as the season progresses, as reflected by decreasing temporary storage and dispersivity. Early onset of melting likely led to formation of an efficient, discrete drainage system early in the melt season, subject to decreasing sinuosity and braiding as the season progressed. Analysis of turbidity-discharge hysteresis further supports the formation of discrete, efficient drainage, with clockwise diurnal hysteresis suggesting easy mobilisation of readily-available sediments in channels. Dye injection immediately downstream of the pollution source zone revealed prolonged storage of dye followed by fast, efficient release. Twinned with a low dye recovery, and supported by sporadic detection of hydrocarbons in the proglacial river, we suggest that meltwater, and thus pollutants in solution, may be released periodically from this zone of the glacier hydrological system. The here identified dynamics of dye storage, dispersion and breakthrough indicate that the ultimate fate and permanence of pollutants in the glacier system is likely to be governed by storage of pollutants in the firn layer and ice mass, or within the internal hydrological system, where it may refreeze. This shows that future studies on the fate of hydrocarbons in pristine, glaciated mountain environments should address the extent to which pollutants in solution act like water molecules or whether they are more susceptible to, for example, refreezing into the surrounding ice, becoming stuck in micro-fractures and pore spaces, or sorption onto subglacial sediments.

On the 15th March 2012 a Royal Norwegian Air Force Lockheed Martin C-130J Super Hercules aircraft crashed into the western face of Kebnekaise (Sweden’s highest mountain) in Lapland, during a military exercise. In addition to five fatalities, the crash deposited some 11000 litres of kerosene jet fuel across the mountain wall, snow and ice, which was then further distributed following a large avalanche triggered by the crash. Debris from the crash has been found on Storglaciären, Björlings glaciär, and near the summit of Kebnekaise, but the majority of debris and fuel was deposited on Rabots glaciär, and the pollution was not subject to any immediate decontamination efforts. While much of the aircraft debris has now been removed during clean-up exercises by the Swedish Military (Figure 1), little was known about the fate of the hydrocarbon pollutants.

Rabots glaciär is subject to ongoing terminus retreat and thinning, and responds more quickly to climatic changes than neighbouring Storglaciären (Brugger, 2007). Although the Rabots glaciär catchment is in a very remote location, the glacier meltwater outlet (proglacial river) feeds rivers used for drinking water by numerous backpackers and the local Sami, who work with reindeer husbandry along the banks of the Kaitum river system. With a possibility for environmental, social and economic impacts arising from water pollution in this region, it is imperative to evaluate the evolution of the polluted area and mechanisms for hydrocarbon pollutant dispersal from the source zone (Figure 2) in the accumulation area of Rabots glaciär. To tackle this, a monitoring programme has been run by researchers at Tarfala Research Station and Stockholm University (led by Gunhild Rosqvist, myself, and Jerker Jarsjö), including repeat sampling in the snowpack, ice/firn, and the proglacial river for chemical analysis to detect jet fuel components. To investigate the pathways and transit times of pollutants from the source zone (Figure 2), a series of dye tracing tests were conducted as a proxy for flow of pollutants in solution through the glacier system (Clason et al., submitted). In these tests an instrument called a fluorometer detects the emergence of the dye in the proglacial river, following initial injection into flowing water above a moulin (Figure 3), a vertical shaft in the ice which provides entry for meltwater to the internal and subglacial drainage systems. Dye tracing experiments provide an indirect method for understanding what the hydrological system inside and underneath a glacier may look like, how fast and efficiently meltwater flows through a glacier, and the extent to which meltwater is stored during its journey through glacier.

Figure 3. Injection of the water tracing dye rhodamine into a supraglacial stream directly above a moulin on Rabots glaciär.

The results of dye tracing revealed likely storage of meltwater and pollutants near the source zone within or beneath the glacier, released in pulses when sufficient water flux from precipitation or melting flushes out the hydrological system. This was supported by infrequent, sporadic detection of pollutants in the proglacier river. The levels of pollutants detected are not thought to currently be a threat to the drinking water supply, but under conditions of higher melting in a warming climate, the frequency and levels of pollution released into the river system could increase. Based on the solubility of the hydrocarbon compounds of the fuel, the lifetime of these compounds in the source zone on Rabots glaciär was modelling with a coupled melt-mass flux modelling approach (Clason et al., in preparation). Assuming no change in summer melting conditions (based on 2013 meteorological data), and perfect contact between the meltwater and the fuel compounds, some of the lighter hydrocarbon compounds have likely already left the glacier. However, heavier components have the potential to persist for tens of thousands of years, far outliving the glacier itself.

Under warming climate scenarios we may see increased interaction of these jet fuel compounds with the surrounding pristine Arctic environment, with potential not only to affect drinking water supplies, but also the local ecosystem and even microbial life on the ice. With increasing use of snowmobiles and helicopters in this region, evaluation of both the long and short term impacts of hydrocarbon pollutants must continue.